Traditional models for functional decomposition of algorithms are vague in their definition of lower decomposition levels. In the Yourdon structured model, control transformations decompose into state transition diagrams which represent the real-time aspects of the system. Although control transformations were used by Yourdon, Ward and Millor, and Hatley and Pirbhai to define real-time control transformation events, their definition of control transformation does not include any of the following types of software statements: goto, if-then-else, switch loops, and subroutine calls.
If the transformations decompose from the highest to the lower levels, but the complexity is not constrained by the developer as the functionality decomposes, as in the McCabe model, the amount of control is unconstrained, and it is not clear when the decomposition should end. Furthermore, since the unconstrained decomposition does not inherently simplify the design, it does not actually meet the criteria of mathematical functional decomposition.